1. Field of the Invention
The present invention relates to brake systems of small transmissions used on riding lawn mowers and the like. In particular, the field of the invention is that of brake lever arrangements for such transmissions.
2. Prior Art
One prior art brake system, used in small transmissions for riding lawn mowers and the like, includes a brake disc which is rotatably coupled to one of the shafts of the drive train. The disc brake system also includes one or more pucks having friction surfaces which are pressed against the brake disc to retard the rotation of one of the drive train shafts and thereby slow the output speed of the transmission. One transmission utilizing a disc brake system is disclosed in U.S. Pat. No. 4,966,574, assigned to the assignee of the present invention, the disclosure of which is explicitly incorporated by reference.
In the brake system disclosed in the '574 patent, a pair of pins is slidably disposed in the housing and may be moved inwardly by brake lever thereby pressing the outer friction puck against the brake disc. The brake lever is pivotally mounted on the housing and includes a cam surface which engages the sliding pins. The interaction of the cam surface and the pins causes the pins to move inwardly and exert pressure on the outer friction puck.
The brake disc has a slight end play which permits it to move axially into abutment with the inner friction puck so that the brake disc is effectively squeezed between the friction pucks upon pivoting of the brake lever. Rotation of the brake disc is retarded when the brake lever is moved into an actuated position, because the cam surface moves the pins which causes the friction pucks to be pressed together and trap the brake disc. The position of the brake lever determines the pressing force of the brake pins and thereby the amount of stopping torque exerted on the brake disc.
However, a problem with any disc brake system is that the brake lever may not return to a position which totally releases the brake disc due to the brake lever's alignment with the vehicle controls. Typically, vehicle controls include a manually operated pedal or lever connected by linkage to the brake lever which is used to actuate and deactivate the application of braking force. The brake lever and the linkage may be connected slightly askew wherein when the linkage releases the brake lever, the brake lever does not move completely to the unactuated position. Further, the brake lever may not align with a plane perpendicular to the axis of the brake lever pivot when in the unactuated position, and thereby keep the pins pressing against the outer friction puck.
The manually operated pedal is often connected to a spring mechanism or other arrangement so that when the operator terminates application of braking force, the brake pedal returns to an unactuated position. However, the spring mechanism moves only the pedal to its original position. The spring mechanism does not positively move and align the brake lever so that the brake lever and the linkage may remain in a skewed arrangement.
Such a skewed arrangement may result in the brake lever returning to a position in which the brake puck drags on the brake disc. This dragging may result from the failure of the actuating mechanism to move the brake lever completely back to the unactuated position. Alternatively, dragging may result from the brake lever being misaligned relative to the plane of rotation which is generally perpendicular to the axis of the brake lever such that the brake pins continue to press the friction pucks into the brake disc. In either circumstance, undesirable frictional contact continues between the friction pucks and the brake disc after the manually operative control has returned to the unactuated position.
This frictional contact generates heat which wears the brake pucks and may require more frequent replacement than brake pucks which are not subject to such frictional contact. Also, dragging creates frictional contact between the puck and disc which may result in a slight slowing of the speed of the transmission.
What is needed is a brake for a small transmission which completely disengages the brake mechanism.
Also needed is a brake for a small transmission which positively moves the brake lever to a non-braking position.
A further need is for brake for a small transmission which is inexpensive to manufacture.
An additional need is for a brake which aligns the brake lever with the plane of rotation.